The present invention relates generally to methods and systems for non-destructive inspection and, more specifically to non-destructive inspection methods and systems for reconstructing internal features of an object.
Reverse engineering is an important approach in product design and manufacturing. Unlike traditional product design, reverse engineering mainly focuses on turning physical models into engineering design concepts or digital models. A typical reverse engineering process includes four major steps. The first step is to measure both internal and external features, and obtain a digital representation of the physical part. After the data is acquired, post processing the data is required, which includes registering data from different measurement systems or view directions, detecting and removing outliers, filtering noise and smoothing the inspection data. Based on the processed data, geometric features are extracted. Finally, a solid model is created based on the extracted geometric representation.
Because the accuracy of the measurement data directly affects the quality of the final model, it is important to select the proper measurement methods and establish an effective measurement strategy. There are various methods, contact and non-contact, to obtain a digital representation of a physical part. Contact methods provide high accuracy but are cumbersome and time consuming. Non-contact methods are generally much faster than the contact methods. Non-contact methods, such as optical metrology, are widely used to measure the external features.
There are many ways to measure external structures of a mechanical part. Coordinate measurement machine (CMM), laser scanners or other optical measurement methods are suitable to obtain such information. But measuring the internal structure of the part is very difficult because of the non-accessibility of the internal structures. Currently, two broad methodologies are primarily employed to measure internal structures. One is a destructive method, involving cutting up the part slice by slice and then measuring each slice to determine the internal features, whereas the other methodology is nondestructive and uses non-intrusive techniques, such as an industrial computed tomography (CT) machine to measure the part. There are drawbacks to both of these methodologies. The destructive method deforms the part before it is measured and fails to capture detailed internal structures. In addition, the part is not re-usable, and intensive labor is involved. Although CT is a nondestructive measurement method, its measurement error is large (greater than 5 mils for most systems), and this low accuracy may lead to inaccuracy in the final model.
It is therefore desirable to measure internal structures with high accuracy using a non-destructive method.